In the drilling and production of offshore wells in many parts of the world, the tension leg platform appears to be an expeditious structure capable of successfully encountering many of the conditions which hamper the operation of the normal type floating or semisubmersible platform. Operationally, the tension leg type unit is maintained in a partially submerged condition by the combination of ballasting and fastoning by way of a series of essentially vertical cables which attach to anchors firmly embedded at the ocean floor.
Such structures tend to minimize roll, pitch and vertical displacement prompted by weather conditions at the drilling area. They are nonetheless operated at a disadvantage in ice infested areas. This is true since the very nature of their hold-down means discourages rapid removal of the platform when it is determined to be in the path of large floating objects, such as icebergs, ice ridges, and the like.
Since such large, natural floating objects, when urged on by wind and wave conditions, tend to be an irresistible mass, the only feasible solution is to temporarily displace the platform from the path of the mass.
To disconnect the ordinary type offshore platform without losing the mooring lines and anchors necessitates the use of boats and auxiliary equipment and is too time consuming for emergency release in areas subject to ice attack. In the instance of a tension leg unit, the same problem exists. In addition, the anchoring lines are under severe tension and cannot merely be cast off, but must be slackened uniformly, and then disconnected from the floating segment of the platform.
Toward permitting the rapid removal of this type platform when endangered by floating objects, each hold-down cable is provided with a self-detaching coupling which forms a connection between the platform and the anchor. So long as the desired tension in the cable is maintained the platform will be held in its desired working position. However, as cable tension is released, the heavy coupling member will assume such a position as to be readily disengaged or to be self-disengaging, thereby in effect to separate the hold-down cable, thus freeing the floating vessel.
It is therefore an object of the invention to provide a tension leg platform which is particularly capable of quick removal from an offshore working site. A further object is to provide hold-down means for a tension leg platform which is readily actuatable to disconnect the floating platform from floor-positioned anchors. A still further object is to provide a coupling means for a hold-down cable which is adapted to self-disconnect at such time as tension within the cable is released, thereby in effect releasing the platform from its restrained position.